화학공학소재연구정보센터
Journal of the American Chemical Society, Vol.119, No.1, 53-58, 1997
Shapes of Dendrimers from Rotational-Echo Double-Resonance NMR
The solid-state shape, size, and intermolecular packing of a fifth-generation dendritic macromolecule were determined by a combination of site-specific stable-isotope-labeling, rotational-echo double-resonance (REDOR) NMR and distance-constrained molecular dynamics simulations. REDOR experiments measured dipolar couplings between C-13 atoms located near the chain ends and an F-19 label placed at the core of benzyl ether dendrimers (generations 1-5) based on 3,5-dihydroxybenzyl alcohol as the monomeric repeat unit. Intramolecular C-13-F-19 coupling was distinguished from intermolecular coupling by dilution with nonlabeled dendrimer. The average intramolecular C-13-F-19 distances for generations 3-5 were each approximately 12 Angstrom, which indicates inward-folding of chain ends with increasing generation number. The average intermolecular C-13-F-19 dipolar coupling decreased with increasing generation number, consistent with decreased interpenetration for larger dendrimers. The measured intra- and intermolecular distances for the fifth-generation dendrimer were used as constraints on energy minimizations and molecular dynamics simulations, which resulted in visualizations of the dendrimer packing and an estimate of density in the solid state.